Memory access module for performing a plurality of sensing operations to generate digital values of a storage cell in order to perform decoding of the storage cell

Abstract

A method for performing memory access of a Flash cell of a Flash memory includes: performing a first sensing operation corresponding to a first sensing voltage to generate a first digital value of the Flash cell; according to a result of the first sensing operation, performing a plurality of second sensing operations to generate a second digital value of the Flash cell representing at least one candidate threshold voltage of the Flash cell; determining the threshold voltage of the memory Flash cell according to the at least one candidate threshold voltage; determining soft information of a bit stored in the Flash cell according to the threshold voltage of the Flash cell; and using the soft information to perform soft decoding.

What is claimed is: 
     
       1. A method for performing memory access of a Flash cell of a Flash memory, comprising:
 performing a first sensing operation corresponding to a first sensing voltage to generate a first digital value of the Flash cell; 
 according to a result of the first sensing operation, performing a plurality of second sensing operations to generate a second digital value of the Flash cell representing at least one candidate threshold voltage of the Flash cell; 
 determining the threshold voltage of the memory Flash cell according to the at least one candidate threshold voltage; 
 determining soft information of a bit stored in the Flash cell according to the threshold voltage of the Flash cell; and 
 using the soft information to perform soft decoding. 
 
     
     
       2. The method of  claim 1 , wherein the plurality of second sensing operations comprise:
 when a result of the first sensing operation is that current flows through the Flash cell, the subsequent second sensing operation will correspond to a sensing voltage which is less than a sensing voltage corresponding to the first sensing operation; and 
 when a result of the first sensing operation is that current does not flow through the Flash cell, the subsequent second sensing operation will correspond to a sensing voltage which is higher than a sensing voltage corresponding to the first sensing operation. 
 
     
     
       3. The method of  claim 1 , wherein the second digital value represents whether at least one candidate threshold voltage of the memory Flash cell is high or low; and the method further comprises:
 determining the threshold voltage of the Flash cell according to whether the at least one candidate threshold voltage is high or low. 
 
     
     
       4. The method of  claim 1 , wherein a number of various possible states of the Flash cell is equal to a number of various possible combinations of all bit(s) stored in the Flash cell. 
     
     
       5. A Flash memory access module for performing memory access management of a Flash storage device comprising a plurality of storage cells, the Flash memory access module comprising:
 a read only memory for storing a program code; and 
 a microprocessor, coupled to the read only memory, for executing the program code to perform the following steps:
 for a Flash cell of the Flash storage device, performing a first sensing operation corresponding to a first sensing voltage to generate a first digital value of the Flash cell; 
 according to a result of the first sensing operation, performing a plurality of second sensing operations to generate a second digital value of the Flash cell representing at least one candidate threshold voltage of the Flash cell; 
 determining the threshold voltage of the memory Flash cell according to the at least one candidate threshold voltage; 
 determining soft information of a bit stored in the Flash cell according to the threshold voltage of the Flash cell; and 
 using the soft information to perform soft decoding. 
 
 
     
     
       6. The Flash memory access module of  claim 5 , wherein the plurality of second sensing operations comprises:
 when a result of the first sensing operation is that current flows through the Flash cell, the subsequent second sensing operation will correspond to a sensing voltage which is less than a sensing voltage corresponding to the first sensing operation; and 
 when a result of the first sensing operation is that current does not flow through the Flash cell, the subsequent second sensing operation will correspond to a sensing voltage which is higher than a sensing voltage corresponding to the first sensing operation. 
 
     
     
       7. The Flash memory access module of  claim 5 , wherein the second digital value represents whether at least one candidate threshold voltage of the Flash cell is high or low; and the microprocessor executes the program code to further perform the step of:
 determining the threshold voltage of the storage cell according to whether the at least one candidate threshold voltage is high or low. 
 
     
     
       8. The Flash memory access module of  claim 5 , wherein a number of various possible states of each Flash cell directly corresponds to a number of various possible combinations of all bit(s) stored in the Flash cell.